Scheme 1. (A) Biosynthesis of 1 and (+)-Neoisomenthol (5) from (S)-4 and (B) Proposed KSI Catalytic Mechanism with 3, on the Basis of the Known Mechanism of the Enzyme towards Δ5-3-Ketosteroids¹⁴.

Abbreviations: L3H = (−)-limonene-3-hydroxylase; IPDH = (−)-trans-isopiperitenol dehydrogenase; IPR = (−)-isopiperitenone reductase; IPGI = (+)-cis-isopulegone isomerase; PGR = (+)-pulegone reductase; MMR = (−)-menthone:(−)-menthol reductase; MNMR = (−)-menthone:(−)-neomenthol reductase.